Bug 840902. Part 1: Stop checking the results of various display list methods. r=mattwoodrow

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extra : rebase_source : 50a3d6809ef76a25a3d02d91f2873d9ba11fdc56
Bug 840902. Part 2: Remove nsresults from various display list methods. r=mattwoodrow

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extra : rebase_source : de498510bf8d85d9b0b2fab0137ef3be01c9adfa